The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. Containers made of plastic, such as polyethylene terephthalate (“PET”), have become commonplace for the packaging of liquid products, such as fruit juices and sports drinks, which must be filled into a container while the liquid is hot to provide for adequate and proper sterilization of the product. Because these plastic containers are normally filled with a hot liquid, the product that occupies the container is commonly referred to as a “hot-fill product,” and the container is commonly referred to as a “hot-fill container.” During filling of the container, the product is typically dispensed into the container at a temperature of at least 180° F. Immediately after filling, the container is sealed or capped, such as with a threaded cap, and as the product cools to room temperature, a negative internal pressure or vacuum forms within the sealed container. Although PET containers that are hot-filled have been in use for quite some time, such containers are not without their share of limitations.
One limitation of PET containers that receive a hot-filled product is that during cooling of the liquid product, the containers may undergo an amount of physical distortion. More specifically, a vacuum or negative internal pressure caused by a cooling and contracting internal liquid may cause the container body or sidewalls to deform in unacceptable ways to account for the pressure differential between the space inside of the container and the space outside, or atmosphere surrounding, the container. Containers with deformations are aesthetically unpleasing and may lack mechanical properties to ensure sustained container strength or sustained structural integrity while under a negative pressure.
Another limitation of PET containers that receive a hot-filled product is that they are not easily held by a hand of a handler, such as a consumer who is drinking the product directly from the container or pouring the product from the container into a smaller container, such as a drinking glass. For instance, intended container gripping areas typically located on the body of containers are not designed to conform to a user's hand or accept specific parts of a user's hand to maximize holding capacity while also accounting for the above-mentioned pressure differential associated with hot-filled containers.
Another limitation of plastic containers, such as hot-fill containers, is that such containers may be susceptible to buckling during storage or transit. Typically, to facilitate storage and shipping of PET containers, they are packed in a case arrangement and then the cases are stacked case upon case, such as on pallets that are then lifted and moved with fork-lifts. While stacked one upon another, each container is capable of buckling and subject to compression upon itself due to the weight of direct vertical loading. Such loading may result in container deformation or container rupture, both of which are potentially permanent, which may then render the container and internal product as unsellable or unusable.
Yet another limitation with hot-filled containers lies in preserving the body strength of the container during the cooling process. One way to achieve container body strength is to place a multitude of vertical or horizontal ribs in the container to increase the moment of inertia in the body wall in select places. However, such multitude of ribs increases the amount of plastic material that must be used and thus contributes to the overall weight and size of the container.